European patents EP 50 742 and EP 69 700, and U.S. Pat. Nos. 2,696,482; 3,597,400; 4,207,411; and 4,369,305, all describe amorphous polyamides made from aliphatic diamines and/or 4,4'-diaminocyclohexylmethane (PCAM) and aromatic dicarboxylic acids. Unfortunately, these polyamides have inadequate tenacity and transparency, and they are not colorless.
Polyamides described in U.S. Pat. No. 2,512,606 and published German Patent Disclosure Application DE-OS 29 34 541, which are made from aliphatic dicarboxylic acids and unsubstituted cycloaliphatic diamines with a high proportion of trans-trans isomer are inadequately resistant to stress cracking in boiling water and alcohols to be commercially useful. Additionally, some of these polymers are cloudy.
Polyamides disclosed in German Patent Disclosure DE 43 10 970 require an especially high proportion of trans-trans isomer of from 35 to 60% of the 4,4'-diaminodicyclohexylmethane, which is attained only by means of special reaction conditions, including with expensive distillative fractionation in producing the diamine. These diamines are thus considerably expensive. They are commercially available under the trade names PCAM 50(R) (DuPont, Wilmington, Del.) and Wondamin(R) (New Japan chemical Corporation, Osaka). Dicycan(R), from BASF, an unsubstituted bis(4-aminocyclohexyl)methane, has similar high trans-trans isomer proportions. While these diamines can be used to prepared polyamides with satisfactory tenacity, their resistance to bending stress and their lack of dimensional stability under elevated temperatures makes shaped articles made form them inadequate for certain applications, such as filter bowls for use under high temperature ranges.
German Patent Disclosure DE 15 95 354 describes a process for preparing crystal-clear polyamides from dicarboxylic acids and a defined isomer mixture of bis(aminocyclohexyl)-propane, which can contain up to 80% caprolactam.
However, this patent expressly mentions that those polyamides that contain dodecanoic acid as the carboxylic acid are subject to clouding.
German Patent Disclosure DE 37 17 928 covers transparent copolyamides of preferably aromatic dicarboxylic acids containing the isomers, no longer available, of bis(4-amino-3-methyl-5-ethylcyclohexyl)methane, which have insufficiently high Tg values. German Patent Disclosure DE 37 28 334 discloses blends of copolyamides of aromatic dicarboxylic acids and a mixture of hexamethylene diamine and PACM. Although these latter copolyamides have modified impact strength, they again have low Tg values.